The role of glycoprotein 96 in the persistent inflammation of rheumatoid arthritis

Zerumbone reduces TLR2 stimulation-induced M1 macrophage polarization pattern via upregulation of Nrf-2 expression in murine macrophages

Hyperuricemia contributes significantly to gout arthritis pathogenesis, which promotes urate crystal deposition in the joints and activates joint-resident macrophages and circulating monocytes to initiate a state of inflammatory arthritis. In the joint, macrophages have an immune defense role where the presence of urate crystals results in the inflammatory mediators secretion, inflammatory cells recruitment to the joint, and shift macrophage population toward M1 pro-inflammatory phenotypes. Current treatment modalities of gout arthritis have side effects that limit their use in the elderly. A novel treatment that targets macrophage polarization to re-establish homeostasis may initiate a drug discovery program of novel disease-modifying agents for gout. Zerumbone (Zer) is a sesquiterpenoid bioactive compound found in the rhizome of Zingiberaceae family and possesses anti-inflammatory, antioxidant, and anti-proliferative activity. Our study hypothesized that soluble uric acid (sUA) and Pam3CSK4 (TLR2 agonist) reduce the anti-inflammatory function of murine M2 bone marrow-derived macrophages and change the expression of M2 genetic markers toward M1 phenotypes. We observed that priming of M2 macrophages with sUA and Pam3CSK4 significantly decreased M2 specific markers expression, e.g., Arg-1, Ym-1, and Fizz-1, enhanced mRNA expression of IL-1β, TNF-α, CXCL2, and iNOS and increased oxidative stress in M2 macrophages, as exhibited by a reduction in Nrf2 expression. We also aimed to study the impact of Zer on reducing the pro-inflammatory effect of sUA in TLR2-stimulated M2 macrophages. We noticed that Zer treatment significantly reduced L-1β and TNF-α production following Pam3CSK4 + sUA treatment on M2 macrophages. Furthermore, Zer reduced the caspase-1 activity without altering cytosolic NLRP3 content in challenged M2 BMDMs. We also observed that Zer significantly enhanced M2-associated marker's expression, e.g., Arg-1, Ym-1, and Fizz-1, and augmented Nrf-2 and other antioxidant proteins, including HMOX1 and srxn1expression following Pam3CSK4 + sUA treatment. We draw the conclusion that Zer is a potentially effective anti-inflammatory treatment for gout arthritis linked to hyperuricemia.

Azithromycin alleviates the severity of rheumatoid arthritis by targeting the UPR component GRP78

BACKGROUND AND PURPOSE

Azithromycin (AZM) is a macrolide antibiotic with well-described anti-inflammatory properties. This study aimed to substantiate the treatment potential of AZM in rheumatoid arthritis (RA).

EXPERIMENTAL APPROACH

Gene expression profiles were collected by RNA sequencing, and the effects of AZM were assessed in functional assays. In vitro and in vivo assays were performed to examine the effects of AZM-mediated blockade of glucose-regulated protein 78 (GRP78). Assays to define the anti-inflammatory activity of AZM using fibroblast-like synoviocytes (FLSs) from RA patients and collagen-induced arthritis (CIA) in DBA/1 mice were performed. Identification and characterization of the binding of AZM to GRP78 was performed using drug affinity responsive target stability assays, proteomics and cellular thermal shift assays. AZM-mediated inhibition of GRP78 and the dependence of the antiarthritic activity of AZM on GRP78 were assessed.

KEY RESULTS

AZM reduced proinflammatory factor production, cell migration, invasion and chemoattraction and enhanced apoptosis, thereby reducing the deleterious inflammatory response of RA FLSs in vitro. AZM ameliorated the severity of CIA lesions as efficiently as the anti-tumour necrosis factor (anti-TNF) biological agent etanercept (ETC). Transcriptional analyses suggested that AZM treatment impairs signalling cascades associated with cholesterol and lipid biosynthetic processes. GRP78 was identified as a novel target of AZM. AZM-mediated activation of the unfolded protein response (UPR) via the inhibition of GRP78 activity is required not only for inducing the expression of C/EBP-homologous protein (ChOP) but also for the activating sterol-regulatory element binding protein (SREBP) and its targeted genes involved in cholesterol and lipid biosynthetic processes. Furthermore, deletion of GRP78 abolished the antiarthritic activity of AZM.

CONCLUSION AND IMPLICATIONS

These findings confirmed that AZM is a therapeutic drug for RA treatment.

Proteins involved in the endoplasmic reticulum stress are modulated in synovitis of osteoarthritis, chronic pyrophosphate arthropathy and rheumatoid arthritis, and correlate with the histological inflammatory score

It is now well recognized that osteoarthritis (OA) synovial membrane presents inflammatory components. The aim of this work is to provide evidence that similar inflammatory mechanisms exist in synovial membrane (n = 24) obtained from three pathologies presenting altogether an inflammatory gradient: OA, chronic pyrophosphate arthropathy (CPPA) and rheumatoid arthritis (RA). Synovial biopsies were first characterized by a histological score based on synovial hyperplasia and infiltration of lymphocytes, plasma cells, polymorphonuclear and macrophages. All biopsies were also analyzed by 2D-nano-UPLC-ESI-Q-Orbitrap for protein identification and quantification. Protein levels were correlated with the histological score. Histological score was in the range of 3 to 8 for OA, 5 to 13 for CPPA and 12 to 17 for RA. Of the 4,336 proteins identified by mass spectrometry, 51 proteins were selected for their strong correlation (p < 0.001) with the histological score of which 11 proteins (DNAJB11, CALR, ERP29, GANAB, HSP90B1, HSPA1A, HSPA5, HYOU1, LMAN1, PDIA4, and TXNDC5) were involved in the endoplasmic reticulum (ER) stress. Protein levels of S100A8 and S100A9 were significantly higher in RA compared to OA (for both) or to CPPA (for S100A8 only) and also significantly correlated with the histological score. Eighteen complement component proteins were identified, but only C1QB and C1QBP were weakly correlated with the histological score. This study highlights the inflammatory gradient existing between OA, CPPA and RA synovitis either at the protein level or at the histological level. Inflamed synovitis was characterized by the overexpression of ER stress proteins.

Baicalin alleviates collagen‑induced arthritis and suppresses TLR2/MYD88/NF‑κB p65 signaling in rats and HFLS‑RAs

Baicalin is a flavonoid isolated from the root of Scutellaria baicalensis with anti‑inflammatory, antioxidant and antiapoptotic pharmacological properties. however, the therapeutic effect of baicalin on rheumatoid arthritis (RA) is not completely understood. The present study aimed to explore the therapeutic potential and mechanisms underlying baicalin in collagen‑induced arthritis (CIA) model rats. CIA was induced in male SD rats. The hind paw thickness and severity of joint injury were monitored to assess the onset of arthritis. At 28 days after the initial immunization, different doses of baicalin were administered once daily via oral gavage for 40 days. The radiologic and pathological alterations were examined using X‑ray, and hematoxylin and eosin staining, respectively. ELISA was employed to measure the serum levels of proinflammatory cytokines. Reverse transcription‑quantitative PCR and western blotting were conducted to determine the expression of toll‑like receptor (TLR)2, myeloid differentiation factor 88 (MYD88) and NF‑κB p65. Baicalin treatment noticeably alleviated radiographic and histologic abnormalities in the hind paw joints of CIA model rats in a dose‑dependent manner. The serum levels of proinflammatory cytokines were significantly decreased in baicalin‑treated CIA model rats compared with vehicle‑treated CIA model rats. The mRNA expression levels of TLR2 and MYD88, as well as the protein expression levels of TLR2, MYD88 and NF‑κB p65 were significantly decreased by baicalin treatment in the synovial tissue of CIA model rats and human RA fibroblast‑like synoviocytes. The results suggested that baicalin may exert a beneficial effect on CIA, which may be mediated by inhibiting the TLR2/MYD88/NF‑κB signaling pathway.

Oligomeric S100A4 Is Associated With Monocyte Innate Immune Memory and Bypass of Tolerance to Subsequent Stimulation With Lipopolysaccharides

Objectives: Most DAMPs in inflammatory diseases are TLR2- and TLR4-ligands and according to the current concept, repeated stimuli would result in tolerance. Aims of the study were to verify this assumption, to investigate whether epigenetic effectors are involved and to explore the situation in rheumatoid arthritis (RA).

Methods: A trained immunity (TI) and tolerance protocol was established using peripheral blood monocytes from healthy donors, β-glucan and lipopolysaccharide (LPS). The training or tolerance capacities of RA-relevant DAMPs were tested.

Results: β-Glucan-, oS100A4-, HMBG1-, and HSP90-pretreated monocytes showed increased IL-6 responses to LPS re-stimulation. β-Glucan, oS100A and tenascin C induced training of monocytes to release more TNFα. In comparison to β-glucan, most DAMPs tested induced less TI, with exception of oS100A4. Monocytes exposed to oS100A4 showed increased IL-1β, IL-6, and TNFα in response to LPS, in spite that both stimulate TLR4. RNASEq upon β-glucan or oS100A4 revealed similar changes in chemokines/cytokines and epigenetic effectors; 17 epigenetic effectors correlated with chemokine/cytokine gene expression; PRDM8 was associated with more chemokine and cytokine transcripts. Knockdown of PRDM8 abolished TI induced by oS100A4. In RA, plasma S100A4 correlated with increased CSF2, and increased PRDM8 transcription in RA monocytes was associated with increased plasma CCL5 and IL-6, as well as therapy-resistance.

Conclusion: Bypass of tolerance by DAMPs might be a phenomenon as important as TI, since it could explain how chronic inflammation can be maintained in spite of an environment with multiple TLR2/TLR4-ligands. In RA monocytes, a PRDM8-dependent TI mechanism could be responsible for sustained chemokine/cytokines levels.

Immunosurveillance of cancer and the heat shock protein-CD91 pathway

The intracellular functions of heat shock proteins (HSPs) as chaperones of macromolecules are well known. Current observations point to a role of these chaperones in initiating and modulating immune responses to tumors via receptor(s) on dendritic cells. In this article we provide an insight into, and a basis for, the importance of these HSP-mediated immune responses in rejecting nascent and emerging tumors.

ER Stress: A Therapeutic Target in Rheumatoid Arthritis?

Diverse physiological and pathological conditions that impact on protein folding of the endoplasmic reticulum (ER) cause ER stress. The unfolded protein response (UPR) and the ER-associated degradation (ERAD) pathway are activated to cope with ER stress. In rheumatoid arthritis (RA), inflammation and ER stress work in parallel by driving inflammatory cells to release cytokines that induce chronic ER stress pathways. This chronic ER stress may contribute to the pathogenesis of RA through synoviocyte proliferation and proinflammatory cytokine production. Therefore, ER stress pathways and their constituent elements are attractive targets for RA drug development. In this review, we integrate current knowledge of the contribution of ER stress to the overall pathogenesis of RA, and suggest some therapeutic implications of these discoveries.

Endogenous ligands of TLR4 promote unresolving tissue fibrosis: Implications for systemic sclerosis and its targeted therapy

Fibrosis, the hallmark of scleroderma or systemic sclerosis (SSc), is a complex, dynamic and generally irreversible pathophysiological process that leads to tissue disruption, and lacks effective therapy. While early-stage fibrosis resembles normal wound healing, in SSc fibrosis fails to resolve. Innate immune signaling via toll-like receptors (TLRs) has recently emerged as a key driver of persistent fibrotic response in SSc. Recurrent injury in genetically predisposed individual causes generation of "damage-associated molecular patterns" (DAMPs) such as fibronectin-EDA and tenascin-C. Sensing of these danger signals by TLR4 on resident cells elicits potent stimulatory effects on fibrotic gene expression and myofibroblast differentiation, and appears to sensitize fibroblasts to the profibrotic stimulatory effect of TGF-β. Thus, DAMPs induce TLR4-mediated innate immune signaling on resident mesenchymal cells which drives the emergence and persistence of fibrotic cells in tissues, and underlies the switch from a self-limited repair response to non-resolving pathological fibrosis characteristic of SSc. In this review, we present current views of the DAMP-TLR4 axis in driving sustained fibroblasts activation and its pathogenic roles in fibrosis progression in SSc, and potential anti-fibrotic approaches for selective therapeutic targeting of TLR4 signaling.

Inflammaging and 'Garb-aging'

'Inflammaging' refers to the chronic, low-grade inflammation that characterizes aging. Inflammaging is macrophage centered, involves several tissues and organs, including the gut microbiota, and is characterized by a complex balance between pro- and anti-inflammatory responses. Based on literature data, we argue that the major source of inflammatory stimuli is represented by endogenous/self, misplaced, or altered molecules resulting from damaged and/or dead cells and organelles (cell debris), recognized by receptors of the innate immune system. While their production is physiological and increases with age, their disposal by the proteasome via autophagy and/or mitophagy progressively declines. This 'autoreactive/autoimmune' process fuels the onset or progression of chronic diseases that can accelerate and propagate the aging process locally and systemically. Consequently, inflammaging can be considered a major target for antiaging strategies.

TLRs, future potential therapeutic targets for RA

Toll like receptors (TLR)s have a central role in regulating innate immunity and in the last decade studies have begun to reveal their significance in potentiating autoimmune diseases such as rheumatoid arthritis (RA). Earlier investigations have highlighted the importance of TLR2 and TLR4 function in RA pathogenesis. In this review, we discuss the newer data that indicate roles for TLR5 and TLR7 in RA and its preclinical models. We evaluate the pathogenicity of TLRs in RA myeloid cells, synovial tissue fibroblasts, T cells, osteoclast progenitor cells and endothelial cells. These observations establish that ligation of TLRs can transform RA myeloid cells into M1 macrophages and that the inflammatory factors secreted from M1 and RA synovial tissue fibroblasts participate in TH-17 cell development. From the investigations conducted in RA preclinical models, we conclude that TLR-mediated inflammation can result in osteoclastic bone erosion by interconnecting the myeloid and TH-17 cell response to joint vascularization. In light of emerging unique aspects of TLR function, we summarize the novel approaches that are being tested to impair TLR activation in RA patients.

The interaction of lubricin/proteoglycan 4 (PRG4) with toll-like receptors 2 and 4: an anti-inflammatory role of PRG4 in synovial fluid

Background

Lubricin/proteoglycan-4 (PRG4) is a mucinous glycoprotein secreted by synovial fibroblasts and superficial zone chondrocytes. PRG4 has a homeostatic multifaceted role in the joint. PRG4 intra-articular treatment retards progression of cartilage degeneration in pre-clinical posttraumatic osteoarthritis models. The objective of this study is to evaluate the binding of recombinant human PRG4 (rhPRG4) and native human PRG4 (nhPRG4) to toll-like receptors 2 and 4 (TLR2 and TLR4) and whether this interaction underpins a PRG4 anti-inflammatory role in synovial fluid (SF) from patients with osteoarthritis (OA) and rheumatoid arthritis (RA).

Methods

rhPRG4 and nhPRG4 binding to TLR2 and TLR4 was evaluated using a direct enzyme linked immunosorbent assay (ELISA). Association of rhPRG4 with TLR2 and TLR4 overexpressing human embryonic kidney (HEK) cells was studied by flow cytometry. Activation of TLR2 and TLR4 on HEK cells by agonists Pam3CSK4 and lipopolysaccharide (LPS) was studied in the absence or presence of nhPRG4 at 50, 100 and 150 μg/ml. Activation of TLR2 and TLR4 by OA SF and RA SF and the effect of nhPRG4 SF treatment on receptor activation was assessed. PRG4 was immunoprecipitated from pooled OA and RA SF. TLR2 and TLR4 activation by pooled OA and RA SF with or without PRG4 immunoprecipitation was compared.

Results

rhPRG4 and nhPRG4 exhibited concentration-dependent binding to TLR2 and TLR4. rhPRG4 associated with TLR2- and TLR4-HEK cells in a time-dependent manner. Co-incubation of nhPRG4 (50, 100 and 150 μg/ml) and Pam3CSK4 or LPS reduced TLR2 or TLR4 activation compared to Pam3CSK4 or LPS alone (p <0.05). OA SF and RA SF activated TLR2 and TLR4 and nhPRG4 treatment reduced SF-induced receptor activation (p <0.001). PRG4 depletion by immunoprecipitation significantly increased TLR2 activation by OA SF and RA SF (p <0.001).

Conclusion

PRG4 binds to TLR2 and TLR4 and this binding mediates a novel anti-inflammatory role for PRG4.

The Role of Damage-Associated Molecular Patterns in Human Diseases: Part I - Promoting inflammation and immunity

There is increasing interest by physicians in the impact of the innate immune system on human diseases. In particular, the role of the molecules that initiate and amplify innate immune pathways, namely damage-associated molecular patterns (DAMPs), is of interest as these molecules are involved in the pathogenesis of many human disorders. The first part of this review identifies five classes of cell stress/tissue injury-induced DAMPs that are sensed by various recognition receptor-bearing cells of the innate immune system, thereby mounting inflammation, promoting apoptosis and shaping adaptive immune responses. The DAMPs activate and orchestrate several innate immune machineries, including inflammasomes and the unfolded protein response that synergistically operates to induce inflammatory, metabolic and adaptive immune pathologies. Two examples of autoimmune diseases are discussed as they represent a typical paradigm of the intimate interplay between innate and adaptive immune responses.

Cell membrane gp96 facilitates HER2 dimerization and serves as a novel target in breast cancer

HER2 receptor dimerization is a critical step in the HER2 activation process. Here, we demonstrated that heat shock protein gp96 on cell membrane interacts with HER2, facilitates HER2 dimerization and promotes cell proliferation. Cell membrane gp96 levels were observed to correlate with HER2 phosphorylation in primary breast tumors. Finally, we provide evidence that targeting gp96 with a specific monoclonal antibody led to decreased cell growth and increased apoptosis in vitro, and suppression of tumor growth in vivo. Our work represents a new therapeutic strategy for inhibiting HER2 signaling in cancer.

Endoplasmic reticulum chaperones and their roles in the immunogenicity of cancer vaccines

The endoplasmic reticulum (ER) is a major site of passage for proteins en route to other organelles, to the cell surface, and to the extracellular space. It is also the transport route for peptides generated in the cytosol by the proteasome into the ER for loading onto major histocompatibility complex class I (MHC I) molecules for eventual antigen presentation at the cell surface. Chaperones within the ER are critical for many of these processes; however, outside the ER certain of those chaperones may play important and direct roles in immune responses. In some cases, particular ER chaperones have been utilized as vaccines against tumors or infectious disease pathogens when purified from tumor tissue or recombinantly generated and loaded with antigen. In other cases, the cell surface location of ER chaperones has implications for immune responses as well as possible tumor resistance. We have produced heat-shock protein/chaperone protein-based cancer vaccines called “chaperone-rich cell lysate” (CRCL) that are conglomerates of chaperones enriched from solid tumors by an isoelectric focusing technique. These preparations have been effective against numerous murine tumors, as well as in a canine with an advanced lung carcinoma treated with autologous CRCL. We also published extensive proteomic analyses of CRCL prepared from human surgically resected tumor samples. Of note, these preparations contained at least 10 ER chaperones and a number of other residents, along with many other chaperones/heat-shock proteins. Gene ontology and network analyses utilizing these proteins essentially recapitulate the antigen presentation pathways and interconnections. In conjunction with our current knowledge of cell surface/extracellular ER chaperones, these data collectively suggest that a systems-level view may provide insight into the potent immune stimulatory activities of CRCL with an emphasis on the roles of ER components in those processes.

Exogenous heat shock protein gp96 ameliorates CD4+CD62L+ T-cell-mediated transfer colitis

BACKGROUND

The heat shock protein gp96 is an endoplasmic reticulum chaperone involved in endoplasmic reticulum stress reactions. gp96 binds antigens and is secreted into extracellular space on cell stress. After reinternalization by antigen presenting cells, antigens can be transferred to major histocompatibility complex molecules. In recent studies, we found induction of gp96 during differentiation of intestinal macrophages, whereas it was absent in intestinal macrophages of patients with Crohn's disease.

METHODS

To study immuno-modulating effects of gp96 in T-cell transfer colitis BALB/c donor mice were injected with 2 × 100 μg gp96. After 1 week, 2.5 × 10(5) CD4+CD62L+ cells were isolated from spleens and injected into severe combined immunodeficiency recipients. Another group received cells from untreated donors and was treated with 100 μg gp96 after transfer. Control groups received cells from untreated donors, or buffer alone.

RESULTS

After transfer of CD4+CD62L+ T cells from gp96-pretreated donors, mice (TBT gp96) showed an initial weight loss, but after 3 weeks, they recovered and reached the starting weight after 5 weeks. Mice treated with gp96 after transfer (TAT gp96) showed a delayed weight loss in comparison with the CD4+CD62L+ group. The histological scores in CD4CD62L mice were 2.6 ± 0.1, in TBT gp96 mice 1.3 ± 0.3 (CD4+CD62L+ versus TBT gp96: P < 0.05) and in mice treated after transfer 1.9 ± 0.1 (CD4+CD62L+ versus TAT gp96: P < 0.05).

CONCLUSIONS

These findings indicate an essential role of gp96 in the maintenance of tolerance against luminal antigens in the intestinal mucosa. The absence of gp96 in intestinal macrophages of patients with Crohn's disease might provoke loss of this tolerance mediating mechanism.

Fas signaling in macrophages promotes chronicity in K/BxN serum-induced arthritis

OBJECTIVE

A nonapoptotic role of Fas signaling has been implicated in the regulation of inflammation and innate immunity. This study was undertaken to elucidate the contribution of Fas signaling in macrophages to the development of arthritis.

METHODS

K/BxN serum-transfer arthritis was induced in a mouse line in which Fas was conditionally deleted in the myeloid lineage (Cre(LysM) Fas(flox/flox) mice). The arthritis was assessed clinically and histologically. Expression of interleukin-1β (IL-1β), CXCL5, IL-10, IL-6, and gp96 was determined by enzyme-linked immunosorbent assay. Bone marrow-derived macrophages were activated with IL-1β and gp96. Cell phenotype and apoptosis were analyzed by flow cytometry.

RESULTS

Arthritis onset in Cre(LysM) Fas(flox/flox) mice was comparable with that observed in control mice; however, resolution was accelerated during the chronic phase. The attenuated arthritis was associated with reduced articular expression of the endogenous Toll-like receptor 2 (TLR-2) ligand gp96 and the neutrophil chemotactic chemokine CXCL5, and enhanced expression of IL-10. Activation with IL-1β or gp96 induced increased IL-10 expression in Fas-deficient murine macrophages compared with control macrophages. IL-10 suppressed IL-6 and CXCL5 expression induced by IL-1β plus gp96. IL-1β-mediated activation of ERK, which regulates IL-10 expression, was increased in Fas-deficient mouse macrophages.

CONCLUSION

Taken together, our findings indicate that impaired Fas signaling results in enhanced expression of antiinflammatory IL-10 and reduced expression of gp96, and these effects are associated with accelerated resolution of inflammation during the chronic phase of arthritis. These observations suggest that strategies to reduce endogenous TLR ligands and increase IL-10 may be beneficial in the treatment of rheumatoid arthritis.

Glutamine suppresses Hsp72 not Hsp90α and is not inducing Th1, Th2, or Th17 cytokine responses in human septic PBMCs

OBJECTIVE

L-Alanyl-glutamine (L-Ala-Gln) is a pharmaco-nutrient commonly used in nutrition regimens due to its immunomodulatory effects. In critically ill patients who are septic, L-Ala-Gln was associated with an increase in mortality. The aim of this study was to investigate whether L-Ala-Gln modulated heat shock protein (Hsp)-72, 90-α, T helper (Th)1, Th2, and Th17 cytokine expression in the peripheral blood mononuclear cells (PBMC) of patients with severe sepsis.

METHODS

Time-dose effects of L-Ala-Gln were compared with those of L-glutamine (L-Gln) and lipopolysaccharide (LPS) and to healthy controls. PBMCs were incubated with 1 or 10 μg/mL LPS, 5 or 10 mM L-Gln, and 5 or 10 mM L-Ala-Gln for different periods of time (0; 4; 24 h) when culture supernatants were harvested.

RESULTS

In both groups, basal Hsp72 increased over time (P < 0.02); Hsp90-α levels declined in controls (P < 0.02) but remained increased in septic patients (P < 0.02), not exhibiting any significant time-response trend. Both Glns suppressed Hsp72 in septic and controls at 10 mM by 4 h (P < 0.045) and Hsp90-α in the control group by 24 h (P < 0.045). LPS did not induce Hsps in either group. L-Ala-Gln did not induce any of the Th1, Th2, and Th17 cytokines in either group.

CONCLUSION

High doses of L-Gln or L-Ala-Gln do not induce any of the Th1, Th2, and Th17 cytokines in either healthy or septic human PBMCs. High Gln doses suppress Hsp72 in septic and control PBMCs. Hsp90-α time-series expression declines, contrasting the increasing trend of Hsp72 in healthy controls. Hsp90-α sustains increased levels in septic supernatants, showing a characteristic longitudinal behavior needed further elucidation.

Do reciprocal interactions between cell stress proteins and cytokines create a new intra-/extra-cellular signalling nexus?

Cytokine biology began in the 1950s, and by 1988, a large number of cytokines, with a myriad of biological actions, had been discovered. In 1988, the basis of the protein chaperoning function of the heat shock, or cell stress, proteins was identified, and it was assumed that this was their major activity. However, since this time, evidence has accumulated to show that cell stress proteins are secreted by cells and can stimulate cellular cytokine synthesis with the generation of pro- and/or anti-inflammatory cytokine networks. Cell stress can also control cytokine synthesis, and cytokines are able to induce, or even inhibit, the synthesis of selected cell stress proteins and may also promote their release. How cell stress proteins control the formation of cytokines is not understood and how cytokines control cell stress protein synthesis depends on the cellular compartment experiencing stress, with cytoplasmic heat shock factor 1 (HSF1) having a variety of actions on cytokine gene transcription. The endoplasmic reticulum unfolded protein response also exhibits a complex set of behaviours in terms of control of cytokine synthesis. In addition, individual intracellular cell stress proteins, such as Hsp27 and Hsp90, have major roles in controlling cellular responses to cytokines and in controlling cytokine synthesis in response to exogenous factors. While still confusing, the literature supports the hypothesis that cell stress proteins and cytokines may generate complex intra- and extra-cellular networks, which function in the control of cells to external and internal stressors and suggests the cell stress response as a key parameter in cytokine network generation and, as a consequence, in control of immunity.